The relationship between pre-pregnancy BMI, gestational weight gain and neonatal birth weight: a retrospective cohort study

Objectives: Maternal pre-pregnancy body mass index (BMI) and gestational weight gain (GWG) have a meaningful impact on pregnancy and perinatal outcomes. The first aim of the study was to analyze the association between pre-pregnancy BMI and the prevalence of small for gestational age (SGA) and large for gestational age (LGA) outcomes. The second aim was to assess the relation- ship between pre-pregnancy BMI combined with gestational weight gain (GWG) and the prevalence of SGA and LGA measurements. Material and methods: The retrospective cohort study was conducted at Jagiellonian University Hospital in Cracow, Po- land from 2016 to 2017. During this time there were 2,123 deliveries. Patients with chronic diseases, multiple pregnancies, fetal defects and incomplete data were excluded. Finally, 474 cases were enrolled. Patients were divided into BMI groups (underweight, normal, overweight and obese) and into GWG groups (inadequate, adequate, excessive). Relationships between maternal BMI, GWG and newborn weight were examined. Results: There was no statistically significant association between maternal pre-pregnancy BMI and prevalence of SGA measurements. However, underweight women with inadequate GWG showed a higher risk to bear SGA babies (OR 5.2, 95% CI 1.57-17.18). Obese women with adequate GWG had higher risk of bearing LGA newborns (OR 5.48, 95% CI 1.15–26.13). High BMI correlated with excessive GWG (overweight: OR 3.0, 95% CI 1.84–3.87; obese OR 2.45, 95% CI 1.1–5.48). Conclusions: There is a considerable risk of giving birth to a SGA newborn for underweight women with inadequate GWG. There is a statistically significant association between maternal obesity and LGA outcomes. Our study shows that redefining the risks of abnormal neonatal weight considering both pre-pregnancy BMI and gestational weight gain can be useful in providing effective prevention during pregnancy.